(1) Field of the Invention
The present invention relates to a liquid-drop ejection apparatus, and more particularly to a liquid-drop apparatus containing a magnetic fluid in a nozzle.
(2) Description of Related Art
As a device for outputting character image information, various types of printer such as impact type (dot type and shuttle type), electrostatic recording type, thermal recording type, ink jet type and laser beam electrophotography type have been put into practical use. With these output devices, compactness, reduction in weight, color representation, no maintenance, low cost, low noise, high speed and high resolution are required. The ink jet type printer meets the requirements such as compactness, reduction in w eight, color representation, low cost and high speed most sufficiently and therefore, expectations are placed on it.
An ink jet head employed in the ink jet type printer has a construction wherein a nozzle connected with a storage device is pressurized by pressurizing means to eject ink as a discharged fluid.
(1)With the ink jet head of this type, however, it is difficult to keep the amount of the discharged fluid constant if the ink present in the nozzle is movable to the storage device at the pressurizing time. Consequently, a nozzle opening/closing means for opening and closing an ink passage in the nozzle is provided between the pressurizing means and the storage device. This mechanical opening and closing of the nozzle easily lead to trouble, thereby having low reliability. In addition, this requires a complicated construction, thereby having a disadvantage of high manufacturing cost of the ink jet head.
(2)With the ink jet head also, properties of the ink in the nozzle change with temperature change even if the nozzle is pressurized under the same pressure. This causes change of the amount of the discharged ink, whereby a recorded image has problems of uneven density or low reproducibility of tones in a multi-tone image.
(3)The discharge opening of the nozzle is open when the apparatus is not operated after the ink is ejected from the nozzle. Therefore, the ink in the nozzle contacts outside air and is dried at the discharge opening, resulting in nozzle plugging.
The three problems mentioned above are not limited to the ink jet head but are common to any liquid-drop ejection apparatus injecting fluid from the nozzle by use of the pressurizing means.
Next, the ink jet type printer is divided into two types, namely, pulse pressure type and bubble jet type. The pulse pressure type is a method wherein liquid drops are ejected without deflection from the nozzle by pressure waves generated by a piezoelectric element. On the other hand, the bubble jet type is a method wherein bubbles are generated by heating a heating resistance element buried in the nozzle and ink drops are ejected from the nozzle using the force with which the bubbles extend.
A head of the above bubble jet type printer has a construction wherein the heating resistance element 102 is buried in the nozzle 101 as shown in FIG. 1. According to the ink ejection principle of this head, bubbles 104 generated within the nozzle 101 by heating the heating resistance element 102 expand as shown in FIGS. 2(a) and 2(b), and the ink 103 is injected from the nozzle 101 by the expanded bubbles as shown in FIGS. 2(c) and 2(d).
However, the bubble jet type printer entails a problem of deterioration of ink because the head is heated by the heating resistance element.